1. Field of the Invention
The present invention relates to a zoom lens system having both a negative lens group and a positive lens group for use in reader printers and the like that project enlargements of microfilm images on a screen and can print copies of the said images.
2. Description of the Related Art
Zoom lenses comprising both a negative lens group and a positive lens group are well known in various forms because theirs is the simplest construction. The arrangement of a negative lens on the reducing side of a second positive lens group has been disclosed in Japanese Patent Application No. 54-78150.
The aforesaid lens system is used in a still camera to provide a trimming effect or to widen the field angle.
On the other hand, the zoom lens system of the present invention is a high-magnification 18.times. to 36.times. lens for use in microfilm reader printers and the like. Conventional microfilm printers use various exchangeable zoom lens systems having various zoom magnification ranges, and the exchangeable lenses must be compatible with the illumination optical system. Therefore, the lens system to be exchanged must have the pupil position on the reducing side extend toward a position in proximity to the image point on the reducing side. Further, the aforesaid lens system must be compact during the entire zoom range so that it can be inserted in the main unit of a microfilm reader printer.